This invention relates to medical devices and, in particular, a system and technique of employing multi-electrode catheters for cardiac mapping and ablation.
Cardiac dysrhythmias are commonly known as irregular heart beats or racing heart. Two such heart rhythm irregularities are the Wolff-Parkinson-White syndrome and atrioventricular (AV) nodal reentrant tachycardia. These conditions are caused by an extraneous strand of conducting fibers in the heart that provides an abnormal short-circuit, pathway for electric impulses normally conducting in the heart. For example, in one type of Wolff-Parkinson-White syndrome the accessory pathway causes the electric impulses that normally travel from the upper to the lower chamber of the heart to be fed back to the upper chamber. Another common type of cardiac dysrhythmias is ventricular tachycardia (VT), which is a complication of a heart attack or reduction of blood supply to an area of heart muscle, and is a life threatening arrhythmia. All these types of dysrhythmias can usually be traced to one or more pathological xe2x80x9csites of originxe2x80x9d or tachycardia foci in the heart.
In the treatment of cardiac dysrhythmias, non-surgical procedures such as management with drugs are favored. However, some dysrhythmias of the heart are not treatable with drugs. These patients are then treated with either surgical resection of the site of origin or by Automatic implantable cardiovertor defibrillator (AICD). Both procedures have increased morbidity and mortality and are extremely expensive. Even AICD needs major surgical intervention. In addition, some patients of advanced age or illness cannot tolerate invasive surgery to excise tachycardia focus which causes dysrhythmias.
Techniques have been developed to locate sites of tachycardia and to disable their short-circuit function. The site of origin of tachycardia is determined by analysis of surface electrocardiogram or intracardiac electrogram signals during states of arrhythmias which may occur spontaneously or be induced by programmed pacing. Once the site of origin or focus is located, the cardiac tissues around the site are either ablated surgically or with electrical energy so as to interrupt abnormal conduction.
For cardiac mapping, several methods of gathering and analyzing surface electrocardiogram or intracardiac electrogram signals are commonly used.
Surface electrocardiogram is one tool in which the electrocardiograms are gathered from as many as twelve surface electrodes attached to various external body parts of a subject. The ensemble of electrocardiograms usually has a definite signature which may be matched to that generally established to associate with a site of origin in a given location of the heart. In this way, it is possible to determine the gross location of a tachycardia site in the heart.
Intracardiac electrogram allows a tachycardia site of focus to be located more accurately. It is obtained by detecting electrical signals within the heart by means of electrodes attached directly thereto.
Gallagher et al., xe2x80x9cTechniques of Intraoperative ELectrophysiologic Mappingxe2x80x9d, The American Journal of Cardiology, volume 49, January 1982, pp. 221-240, disclose and review several methods of intraoperative mapping in which the heart is exposed by surgery and electrodes are attached directly to it. In one technique, the electrodes at one end of a roving catheter are placed on a series of epicardial or endocardial sites to obtain electrograms for mapping earliest site of activation with reference to surface electrocardiograms. For endocardial mapping, a cardiotomy may also be necessary to open the heart to gain access to the endocardium.
Gallagher et al., supra, also disclose a technique for simultaneous, global mapping of the external surface of the heart (epicardial mapping). A lattice of about 100 electrodes in the form of a sock is worn on the heart, thereby enabling multiple sites to be recorded simultaneously. This technique is particular useful for those cases where the ventricular tachycardia induced is unstable or polymorphic.
Global mapping by means of large array of electrodes has been further disclosed in the following two journal articles: Louise Harris, M.D., et al., xe2x80x9cActivation Sequence of Ventricular Tachycardia: Endocardial and Epicardial Mapping Studies in the Human Ventricle,xe2x80x9d Journal of American College of Cardiology (JACC), Vol. 10, November 1987, pp. 1040-1047; Eugene Downar, et al., xe2x80x9cIntraoperative Electrical Ablation of Ventricular Arrhythmias: A xe2x80x9cClosed Heartxe2x80x9d Procedure,xe2x80x9d JACC, Vol. 10, No. 5, November 1987, pp. 1048-1056. For mapping the interior surface of the heart (endocardial mapping), a lattice of about 100 electrodes in the form of a inflatable balloon is placed inside the heart after cutting it open. Under some situations, a xe2x80x9cclosed heartxe2x80x9d variation may be possible without the need for both a ventriculotomy and ventricular resection. For example, with the subject on cardiopulmonary bypass, a deflated balloon electrode array is introduced into the left ventricular cavity across the mitral valve. Once inside the ventricle, the balloon is inflated to have the electrodes thereon contacting the endocardium.
While the sock or balloon electrode arrays allow global mapping by acquiring electrogram signals over a wider area of the heart simultaneously, they can only be installed after open-chest surgery.
Catheter endocardial mapping is a technique for mapping the electrical signals inside the heart without the need for open-chest or open-heart surgery. It is a technique that typically involves percutaneously introducing an electrode catheter into the patient. The electrode catheter is passed through a blood vessel, like femoral vein or aorta and thence into an endocardial site such as the atrium or ventricle of the heart. A tachycardia is induced and a continuous, simultaneous recording made with a multichannel recorder while the electrode catheter is moved to different endocardial positions. When a tachycardia focus is located as indicated in intracardiac electrogram recordings, it is marked by means of a fluoroscope image. Catheter endocardial mapping are disclosed in the following papers:
M. E. Josephson and C. D. Gottlieb, et. al., xe2x80x9cVentricular Tachycardias Associated with Coronary Artery Disease,xe2x80x9d Chapter 63, pp. 571-580, CARDIAC ELECTROPHYSIOLOGYxe2x80x94from cell to bedside, D. P Zipes et al, Editors, W. B. Saunders, Philadephia, 1990.
M. E. Josephson et al., xe2x80x9cRole of Catheter Mapping in the Preoperative Evaluation of Ventricular Tachycardia,xe2x80x9dThe American Journal of Cardiology, Vol. 49, January 1982, pp. 207-220. Linear multipolar electrode catheters are used in preoperative endocardial mapping.
F. Morady et. al., xe2x80x9cCatheter Ablation of Ventricular Tachycardia With Intracardiac Shocks: Results in 33 Patients,xe2x80x9d CIRCULATION, Vol. 75, No. 5 May 1987, pp. 1037-1049.
Kadish et al., xe2x80x9cVector Mapping of Myocardial Activation,xe2x80x9d CIRCULATION, Vol. 74, No. 3, September 1986,pp. 603-615.
U.S. Pat. No. 4,940,064 to Desai discloses an orthogonal electrode catheter array (OECA). Desai et al., xe2x80x9cOrthogonal Electrode Catheter Array for Mapping of Endocardiac Focal Site of Ventricular Activation,xe2x80x9d PACE, Vol. 14, April 1991, pp. 557-574. This journal article discloses the use of an orthogonal electrode catheter array for locating problem sites in a heart.
Upon locating a tachycardia focus, ablation of cardiac arrhythmias is typically performed by means of a standard electrode catheter. Electrical energy in the form of direct current or radiofrequency is used to create a lesion in the endocardiac tissues adjacent (i.e. underneath) the standard electrode catheter. By creating one or more lesions, the tachycardia focus may be turned into a region of necrotic tissue, thereby disabling any malfunctions.
Existing catheter mapping techniques typically rely on analysis of recorded electrograms. Locating the site of origin and tracking the whereabouts of the catheter are at best tricky and time-consuming, and often proved unsuccessful.
Thus, it is desirable, to have a catheter mapping and ablation system with precision and speed and able to provide comprehensive guidance on a real-time basis.
Accordingly, it is a general object of the present invention to treat ventricular tachycardia and other cardiac dysrhythmias by improved catheter mapping and ablations.
It is an object of the present invention to provide a system which is capable of rapid and accurate cardiac mapping.
It is another object of the present invention to provide a system which is capable of efficiently and accurately locating and ablating a site of origin of tachycardia.
It is another object of the present invention to provide accurate guidance for efficiently and accurately ablating an endocardial site by filling it with successive catheter ablations of a smaller area.
It is yet another object of the present invention to provide real-time visual maps indicating the relative positions of the electrodes, the tachycardia site of origin and the heart.
These and additional objects are accomplished by a system including a multi-electrode catheter selectively connectable to a mapping unit, an ablation unit and a pacing unit. The system also includes a computer for controlling the various functional components. In one embodiment the system additionally includes a physical imaging unit which is capable of providing different views of a physical image of the multi-electrode catheter percutaneously introduced into the heart of a subject.
Electrogram signals emanated from a tachycardia site of origin in the endocardium are detectable by the electrode array. Their arrival times are processed to generate various visual maps to provide real-time guidance for steering the catheter to the tachycardia site of origin.
In one embodiment, the visual map includes a footprint of the electrode array on an endocardial site. The arrival time registered at each electrode is displayed in association therewith. A medical practitioner can therefore steer the catheter in the direction of earlier and earlier arrival time until the tachycardia site of origin is located.
In another embodiment, the visual map also includes isochrones which are contours of equal arrival time. These isochrones are constructed by linear interpolation of arrival times registered at the electrode array and cover the area spanned by the electrode array. When the electrode array is far from the tachycardia site of origin, the isochrones are characterized by parallel contours. When the electrode array is close to or on top of the tachycardia site of origins, the isochrones are characterized by elliptical contours encircling the tachycardia site of origin. Therefore, the isochrones provide additional visual aid and confirmation for steering the catheter to the tachycardia site of origin.
In another preferred embodiment, the visual map also includes an estimated location of the tachycardia site of origin relative to the electrode array. This provides direct visual guidance for rapidly steering the catheter to the tachycardia site of origin. The tachycardia site of origin lies in the weighed direction of electrodes with the earliest arrival times. The distance is computed from the velocity and time of flight between the site of origin and a central electrode. The velocity is estimated from a local velocity computed from the inter-electrode spacings and arrival time differentials.
According to another aspect of the invention, the system also include a physical imaging system which is capable of providing different imaged physical views of the catheter and the heart. These physical views are incorporated into the various visual maps to provide a more physical representation.
In one embodiment, two visual maps display two views (e.g., x,y axes) of a physical image of the electrode array in the heart with a relative position for the tachycardia site of origin.
In another embodiment, a visual map display a three-dimensional perspective view of the electrode array in the heart with a relative position for the tachycardia site of origin.
In yet another embodiment, the visual map also marks previous sites or tracks visited by the electrode array.
With the aid of the visual maps, the electrode array can locate the tachycardia site of origin rapidly and accurately. The system then directs electrical energy from the ablation power unit to the electrode array to effect ablation.
Additional objects, features and advantages of the present invention will be understood from the following description of the preferred embodiments, which description should be taken in conjunction with the accompanying drawings.